> However, all that said, I'm not aware of any instance where the GPL has been
> tested in court (or even "out of court" as they say) against a company
> accused of taking GPL code and developing closed source products from it.
Read "Enforcing The GPL" I and II at <http://emoglen.law.columbia.edu/>.
Apparently the GPL has been tested out of court several times, and
Moglen claims it has never been tested *in* court precisely because it
is so watertight.
GPL has the nicely recursive feature of being considerably less
restrictive that the normal license agreements from which the rest of
the software industry makes its money, so if anyone managed to get GPL
challenged, all such licenses would be suspect. As the only group likely
to be so motivated is precisely that same software industry, this won't
be happening any time soon. :)